My girlfriend purchased a webcam from eBay awhile back and it worked relatively fine when she had dial up but the minute she got broadband the picture the cam showed was just interference (like you get on terrestrial TV's). The cam showed a correct image on the Web Cam Settings on MSN but not once the camera is viewing on a MSN convo.

She is using MSN 7 and all I know about the camera is that it is a USB one.

She has tried reinstalling MSN and the camera to no avial.

Can anyone please help?

You can turn down the picture quality/size on some Cameras to allow the computer to keep up.Broadband is faster but takes more computing power to maintain a live conversation.Is her computer up to date(powerful enough)
Cable broadband can also slow down depending on how many people she must share with.
Have the latest drivers been installed for the camera?
Turn off all unnecessary applications.
Also there can be conflicting issues with signal from the individual you are online with(This is less likely).